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Table 3 Comparison of articles identified through Science Citation Index and PubMed searches until the end of 2003

From: Searching for observational studies: what does citation tracking add to PubMed? A case study in depression and coronary heart disease

Search method(s) that identified article PubMed and Science Citation Index (n = 31) Science Citation Index only (n = 11) PubMed only (n = 8)
   Mean (s.d.) 1999 (6.4) 1996 (7.9) 1997 (9.9)
   Median (range) 2002 (1969–2003) 2001 (1982–2003) 2001 (1973–2002)
Impact factor    
   Mean (s.d.)* 4.2 (2.8) 9.5 (9.8) 3.9 (2.6)
   Median (range) 3.2 (1.1–10.5) 3.8 (2.0–31.7) 2.8 (1.3–7.6)
Study Type 8 aetiologic 23 prognostic 3 aetiologic 8 prognostic 2 aetiologic 6 prognostic
Classification of outcome** 25 positive 6 null 5 positive 6 null 6 positive 2 null
Sample size: aetiologic studies    
Mean (s.d.) 4502 (3331) 5758 (4397) 1101 (1089)
   Median (range) 3269 (76–9758) 7217 (817–9239) 1101 (332–1870)
Sample size: prognostic studies    
Mean (s.d.) 525 (626) 832 (925) 399 (441)
   Median (range) 344 (30–2885) 552 (58–2320) 288 (66–1250)
  1. * Four articles were published in journals with no impact factor (1 both methods, 1 Science Citation Index only, 2 PubMed only).
  2. **Statistically significant result at the p < 0.05 level.